# Questions tagged [computational-geometry]

Questions about algorithmic solutions of geometric problems, or other algorithms making usage of geometry.

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### Recognizing a trajectory from a set

Given a set of 2d trajectories/paths, where a trajectory is a list of [x,y,time] coordinates, and a new trajectory, how can I recognize which one in the set is most similar to it? The lists may not be ...
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### Number of double wedges containing a point

We have a set of $n$ double wedges on a plane. (By double wedge, I mean two lines intersecting at a point, with opposite sides of the point considered as "inside" the double wedge.) Now these $n$ ...
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### CLRS closest-pair $L_m$ distances

I am studying algorithms and datastructures, and in CLRS chapter 33.4, the exercise 33.4-4 states the following: We can define the distance between two points in ways other than euclidean. In the ...
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### Data structure to query intersection of a line and a set of line segments

We want to pre-process a set $S$ of $n$ line segments into a data structure, such that we can answer some queries: Given a query line $l$, report how many line segments in $S$ does it intersect. It ...
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### Robust two lines/segments intersection point in 2D

Given two line segments the problem is to find an intersection point of corresponding lines (assuming that they are not parallel or coincide). There is a Wikipedia article which gives us exact ...
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### Separating the snakes

In a two-dimensional grid, there are $n$ "snakes" (sets of contiguous grid-blocks). The snakes do not touch each other. The goal is to cut the grid into $n$ rectangles using $n-1$ "fences" (horizontal ...
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### Status on Naoki Katoh's “Rectangle Wiring Problem”?

I have found this interesting problem in graph theory and geometry which is allegedly an open problem but latest status seems to be from 01/25/02. I can't see to find any more information about it, ...
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### Find vertices of a convex polytope, defined by intersecting half-spaces

I am looking for a algorithm that returns the vertices of a polytope if provided with the set of intersecting half-spaces that define it. In my special case the polytope is constructed by the ...
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### Interpolation: How to generate 3D objects from 2D cross-sections?

Consider a sphere sitting on an $xy$-plane, and take 2D slices parallel to the $xy$-plane at various heights of z. Suppose we take 10 slices, evenly spaced along the $z$-axis, and now have 10 images ...
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### Convert a polygon mesh into a b-spline surface

$\textbf{Problem:}$ Getting a $\textit{polygon-mesh}$ as input, I have to construct a surface that looks exactly to the given input. My task is to generate a $\textit{b-spline}$ surface that exactly ...
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### Triangulation of disjoint line segments

Given a set of disjoint line segments in the plane, prove (or disprove) that you can always join the line segments to make a near-triangulation where the vertices are the endpoints of the segments, ...
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### Joining line segments to make tree

Given a set of disjoint line segments in the plane, prove (or disprove) that we can always join the line segments to make a tree where the vertices of the tree are the endpoints of the segments and ...
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### Prove vertices of polygon are endpoints of disjoint line segments

If we are given a set of disjoint line segments in the plane, can we prove (or disprove) that we can always join the line segments to make a simple polygon where the vertices of the polygon are the ...
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### Near Triangulation Planar Graph

This is the problem I am dealing with: Given a set P of n points in general position, let a graph G be defined as follows: The vertex set is P. Two vertices, a and b, are joined by an edge provided ...
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### Voronoi Diagram Drawing Variations and Charateristics

I am learning about Voronoi diagrams and I have seen that the Voronoi diagram of a set of points is drawn with straight line segments and rays. Similarly how can we draw the Voronoi diagram for the ...
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### Voronoi Cell and Voronoi Diagram

Consider a set R of n red points and B of n blue points in the plane. Let x∈R and y∈B be the shortest edge xy. Let P = R ∪ B. Let Vor(P) be the Voronoi diagram of P. Let V(x) be the Voronoi cell of x ...
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### Placing a tripod in a plane such that it partition a given set of points (with pic)

I would appreciate if anyone could help me with the following problem: Given a set of 3n points in the plane with n > 0, is it possible to find a placement of a tripod such that each region contains ...
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### Dynamic length of union of segments (1d Klee's measure problem)

Finding the length of union of segments (1-dimensional Klee's measure problem) is a well-known algorithmic problem. Given a set of $n$ intervals on the real line, the task is to find the length of ...
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### Rectangle Packing with Constraints

I am aware that the general rectangle packing problem is NP-hard. I am trying to form an estimate for a version of the problem with constraints. Consider fitting rectangles of smaller size into a ...
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### Upper (or lower) envelope of some linear functions

Given some single variable linear functions $y_1=m_1x+b_1$, $y_2=m_2x+b_2$, $\ldots$, $y_n=m_nx+b_n$, the upper envelope is the function $f(x)= \max \{y_1, \ldots, y_n\}$. We know that this function ...
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### How to devise an algorithm to generate a random but valid train track layout?

I am wondering if I have quantity C of curved tracks and quantity S of straight tracks, how I could devise an algorithm, (computer assisted or not), to design a "random" layout using all of those ...
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### Can we find the largest intersecting subfamily of convex polygons in quadratic time?

Let $\mathcal{F} = \{P_1, P_2,\ldots,P_m\}$ be a family of (closed) convex polygons in the plane, each represented by their vertices in (say) clockwise order. Let $n$ be the total number of vertices (...
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### Minimal set of inequalities including good points but excluding bad points

Suppose I have a collection of good convex sets and bad convex sets in $\mathbb{R}^d$ (where $d$ can be big). Each convex set is defined by a series of closed ranges in each dimension $d$ - a ...
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### Is there a way to perform calculations of Mandelbrot set using only integer numbers?

I would like to create program in JavaScript (JS) which draws Mandelbrot set with arbitrary precision (zoom). In JS there is build in integer type BigInt which support simple operations like +,*,/,...
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### Distance from high dimensional convex hull to target point T

I have a set S of high dimensional points in Euclidean space, with convex hull H (not known); and some target point T in that space not in or on H. Rather than worry about calculating both H and the ...
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### Algorithm for animating/morphing convex polygon diagrams

I am trying to find an algorithm to smoothly morph a (given) diagram made of convex polygons into another (given) diagram of the same type. The target diagram is usually generated from the source, ...
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### O(n) external intersection points?

I have a doubt. For a given n (axis-parallel) squares in a plane, where there are Ω(n²) intersection points between the edges of the square, is it possible to have O(n) external intersection points? (...
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### Data structure to report all axis aligned bounding boxes intersecting an axis aligned query line

I would like to build a Data structure that uses subquadratic space to quickly report a set of AABBs (axis aligned bounding boxes) in 3 dimensional space when it intersects a query line? I am only ...
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### Given a set of (x,y) coordinates, give the set of edges to draw a simple polygon

Let's say I give you the following array of points: (1,1) (1,3), (2,2), (4,1), (4,3) My (terrible) mspaint drawing of the shape that would be created by these looks like this: How, given an ...
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### Given a DCEL, how do you identify the unbounded face

I have constructed a DCEL using the procedure described in How do I construct a doubly connected edge list given a set of line segments?. This correctly identifies all faces, however I'm struggling ...
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### Is there a way to *round* a nearby point into the feasible set?

Let $P \subset \mathbb R^d$ be a polytope with interior given by $F$-many linear inequalities. Suppose we have a convex problem with feasible set $P$. For example computing the Euclidean projection of ...
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### How Expensive is Projecting onto a Polytope?

I have a problem where our action set is a polytope $\mathcal P\subset \mathbb R^d$ and an algorithm that involves projecting onto the action set. For example it says to select the Euclidean ...
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### How can I determine if two vertices on a polygon are consecutive?

Suppose I have a set of points that construct a convex polygon in the Cartesian plane with the points as its vertices. I randomly choose two vertices and want to know if they are consecutive vertices ...
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### RGBD alignment without explicit transformation between RGB and depth

I have a set of RGB-D scans of the same scene, corresponding camera poses, intrinsics and extrinsics for both color and depth cameras. RGB's resolution is 1290x960, depth's is 640x480. Depth is ...
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### What is the name of this problem (the dual of the asymmetric k-center problem)

I know $k-center$ problem is, given $n$ cities with specified distances, one wants to build $k$ warehouses in different cities and minimize the maximum distance of any city to a warehouse. In this ...
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### How to find a path in maze with navigator physical size constraints?

Assuming a 2D maze, how would one go about solving it for rigid 2D object moving through it? Additional specification: The object shape - it is a single entity, not a swarm/fleet. A shape of ...
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### Efficient data structure for matching 3D lines

I'd like to Store a set of many infinite undirected 3D lines. Make lookups against this set - i.e. given an arbitrary line, ask "Does the set contain a line coincident with this one?" The incidence-...